The present invention relates generally to digital communication networks, and more specifically, to Ethernet transport over a Sonet path.
SONET/SDH and optical fiber have emerged as significant technologies for building large scale, high speed, Internet Protocol (IP) based networks. SONET and SDH are a set of related standards for synchronous data transmission over fiber optic networks. SONET is short for Synchronous Optical Network and SDH is an acronym for Synchronous Digital Hierarchy. SONET/SDH is currently used in wide area networks (WAN) and metropolitan area networks (MAN). A Sonet system consists of switches, multiplexers, and repeaters, all connected by fiber. The connection between a source and destination is called a path.
One standard that describes the interconnection of computer devices in network communication is IEEE (Institute of Electrical and Electronic Engineers) standard 802.3, commonly referred to as Ethernet (also adopted as International Standard ISO/IEC 8802-3). The Ethernet system includes an Ethernet frame that consists of a standardized set of bits used to carry data over the system.
Ethernet transport over Sonet products typically map one or more Ethernet ports to a Sonet path for transport across a Sonet network. There is typically an Ethernet transport over Sonet product at each end of a Sonet path. A method is needed for the Ethernet over Sonet transport path to behave transparently, so that its behavior emulates a direct Ethernet connection between end stations connected to the Ethernet over Sonet equipment.
The implementation should also be resilient to Sonet switches (i.e., from UPSR, BLSR, etc.), within the path which can cause traffic disruption. In order to do this, the implementation should provide for minimal frame loss during Sonet switches. Also, it should not bring down links during a Sonet switchover unless there is a permanent failure condition within the Sonet transport path.
Conventional methods of determining whether a remote end station is down (i.e., loss of Ethernet transport) are performed through layer 2 connection level protocols such as PPP signaling. However, this is inefficient and often requires overhead for implementing additional protocols. Other solutions may indicate a local port down state to the remote port by driving AISP on the Sonet path. This method may result in a technician assuming that there is a Sonet circuit failure within the network, when there is actually no circuit failure. Other solutions may also be affected by a Sonet switch within the path. This can cause extraneous link up and down cycling which is detrimental to the data network attached to the Ethernet over Sonet transport path. These solutions typically do not provide a method for quickly shutting off the flow of input Ethernet traffic at the first detection of a local or remote Sonet path failure.